1. Field of the Invention
The present invention relates to a stapler unit for binding a stack of sheets with staples and a sheet processing device for receiving sheets of paper and for binding a received stack of sheets by using the stapler unit.
2. Description of the Related Art
Hitherto, a stapler for automatically stapling a stack of sheets (hereinafter referred to as a sheet stack) has been provided with staples of only one length. When the sheet stack is thick, the staples do not pass through the sheet stack and the sheet stack is stapled incompletely. Therefore, a permissible value for the number of sheets is set, whereby a sheet stack having a number of sheets exceeding the permissible value is left unstapled.
A stapler is disclosed in, for example, Japanese Utility Model Publication No. 3-25931, which receives a detachable cartridge containing a plurality of staple sheets and drives the staples one by one from the staple sheets fed from the cartridge. This stapler is provided with staple sheets of staples having a predetermined length to be applied to a plurality of thicknesses of sheet stacks, and a cutter for cutting an excess part of each staple so as to improve the appearance when the staple protrudes excessively from a thinner sheet stack.
Various staple sorters and finishers have been devised as sheet processing devices. A finisher provided with the stapler disclosed in Japanese Utility Model Publication No. 3-25931 described above is disclosed in, for example, Japanese Patent Laid-Open No. 8-268640. Manipulation of cut-off staples in one of these devices is described below with reference to FIGS. 21A, 21B, and 21C.
A stapler 500 is provided with a shooter 500b at an end thereof for feeding cut-off staples from a predetermined position to a cut-off-staple hopper 500c included in the sheet processing device.
The cut-off staples are received by the hopper 500c via a slope 500g of a needle guide 500f when an aperture 500d of the shooter 500b is opened by being brought into contact with a protruding part 500e of the needle guide 500f. 
The following problems have been found in the known device.
(1) Since staples of only one length are provided, the range of the permissible quantity of sheets to be included in one stack is limited.
(2) A cut-off-staple receiving part must be disposed outside the stapler. Therefore, the stapler must move translationally so as to smoothly transfer the cut-off staples to the cut-off-staple receiving part. Therefore, it is impossible to apply a staple inclined with respect to the edge of the sheet stack.
(3) Sheet stacks with a smaller quantity of sheets are processed more often than sheet stacks with a larger quantity of sheets. Therefore, cut-off staples are produced in almost every manipulation of sheet stacks, thereby contributing to environmental problems.
(4) The cut-off staples received by the cut-off-staple receiving part must be manually removed, which is burdensome. Moreover, the receiving state (quantity of received cut-off-staples) must be detected, thereby increasing the cost and size of the apparatus.
Accordingly, it is an object of the present invention to provide a stapler unit and a sheet processing device using the stapler unit, in which a sheet stack can be stapled without producing cut-off staples regardless of the quantity of stacked sheets.
To these ends, according to an aspect of the present invention, a stapler unit includes a stapler provided with a stapling device for stapling a sheet stack, and a staple cartridge arrangement detachably loaded on the stapler and provided with a staple receiving device for receiving staples. A plurality of the staple cartridges for receiving staples having different lengths are provided in the staple cartridge arrangement, and each of the staple receiving devices of the plurality of staple cartridges is provided with a guide for controlling, when the staple cartridge is loaded, staples received therein so that the longitudinal centers of the staples are positioned at the same positions as those of the staples having other lengths.
With this arrangement, the stapling device included in the stapler can be commonly used for staples of different lengths, and can staple a sheet stack of any quantity of sheets without producing cut-off pieces of staples.
The stapler is provided with a plurality of the staple cartridges for receiving staples having a plurality of lengths. An erroneous operation can be avoided in which a sheet stack having a greater or smaller thickness is processed with staples of a different size. This is possible by providing a -cartridge determining device for determining, when the staple cartridge is loaded, the length of each staple included in the staple cartridge being loaded.
A stapler unit according to the present invention can staple a sheet stack without producing cut-off pieces of staples regardless of the thickness of the sheet stack, whereby an additional device such as a staple cutter in the staple unit is not required. Therefore, the cost of the staple unit can be reduced, and an environmentally friendly product is provided.
An erroneous operation can be avoided in which a sheet stack having a greater or smaller thickness is processed with staples of a different size, by providing a cartridge determining device for determining, when the staple cartridge is loaded, the length of each staple included in the staple cartridge being loaded. With this arrangement, the reliability of the sheet processing device can be maintained, and devices such as a cut-off-staple receiving device and a sensor for detecting a cut-off-staple received state are not required, thereby reducing the cost and the size of the stapler unit.
Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings.